Fluid system



D. MCMAHAN FLUID SYSTEM Original Filed May 22, 1935 Inventor: Kenton D. Mc Mahan,

, v 4 1 by f-l miovneg.

UNITED STATES Patented Oct. 12, 1937 PATENT OFFICE FLUID sYsfraM Kenton Di McMahan, Scotia, N. Y.,assignor to General Electric Company, a corporation oi New York Original application May 22 1935, Serial No. 22,751. Divided and this application November 18, 1936, Serial No. 111,443

as the present invention, and a specific objectof the-invention to which the present application is directedisthe provision of an improved ventilation system incorporating the variable impedance fluid flow control apparatus described in detail andbroadlyclaimed inmy above referred to pending application for controlling the'circulation of air through, and thereby the temperature within, anenclosure. i

A more specific object of the present invention is the provision in a ventilation system of improved apparatus for controlling automatically the proportions of fresh and recirculated air supplied to an enclosure in accordance with variations in apredetermined condition within the enclosure. i 1

Both with; respect to the broader aspects oi? my invention as set forth in my previously: referred to application and the more specific aspects of the invention asset forth in the present applicatiomit maybe stated that-the invention consists generally in theprovision in a fluid system of ,a duct and a plurality of orifices arranged in such cooperating relationship therewith that underone set of pressure conditions fluid is delivered from a single source, or from one of two independent sources, through certain of the oriflees to the duct in such manner that a minimum of contraction is produced in the fluid stream entering the duct and the efliciency of conversion of velocity head to static head is a maxi mum; and that, under another set of pressure conditions, fluid is delivered from the single source, or from the other of the two independent sources asthe case may be, through certain. others of the orifices to the duct in such manner Further objects of my invention and the details of the manner in which the, invention may be carried out will become apparent from the 'following description taken in conjunction with the 1 accompanying drawing in which Fig. ldiagrammatically illustrates in section a ventilation system incorporating the present invention and Figs. 2 and 3 diagrammatically illustrate in longitudinal section the general form and arrangement 01' 9. portion of the apparatus for controlling fluid flow in accordance with the present invention, 5

the form of fluid flow under difierent conditions being represented in the figures by arrows.

Referring particularly to Fig. 1 of the drawing,

- the element designated l0 represents an electric discharge device whichis excited from electric l0 supply line H and which" gives off heat during operation. It is to be understood that such a device is shown for purposes of illustration only and there may be substituted therefor any other heat dissipating device the temperature of which 1 it is desired to maintain within given limits by the circulation of air thereover. The heat dissipating device isenclosed by means of a casing I2 which is provided with air intake and exhaust means illustrated as being in the form of ducts 20 I3 and II respectively. These ducts are so con structed that their open ends are in spaced apart opposed relationship. Duct l3is provided with an inwardly converging bell-shaped inlet opening I! which facilitates the smooth flow of air there- 25 into.

In order thatthe temperature within casing it may be maintained within desired limits, there is provided a duct l6 and an arrangement of orifices and fans for controlling the proportions of fresh 30 inlet l5 of duct l3 and isspaced therefrom as indicated at l9. For best operation of the apparatus it is preferable, though not necessary, that 40 the outlet I! of duct l6 beof equal or slightly greater area than that of the inlet iii of duct it. The throat I! of duct l6 extends into atmosphere. Duct i6 constitutes one form of a diffuser which is a device well known in theart for con- 45 vertingvelocity head of a fluid stream into static head. In order that such a diffuser be eflicient in its operation, its structural characteristics must be such that the outer portions of a fluid stream flowing therethrough follow along the 50 sides thereof in the form of substantially continuous unidirectional streams. In other words, the circumferential flow must be substantially laminar without the formation of eddies along the inner surfaces of the diffuser. To make the 55 fluid follow the sides, the cross-sectional area of the diffuser must increase relatively gradually, and there must be no conditions present which cause eddies to form at the inlet of the diffuser. In accordance with well known principles, the walls of the diffuser illustrated are made to have an angle with the axis of the diffuser which is less than that at which the outer laminae of a fluid stream entering the throat i'l substantially uniformly distributed across the area of the throat with all portions thereof flowing at substantially equal velocity and along lines substantially parallel to the axis of the diffuser, will cease to contact the walls of the diffuser. As is well known to one skilled in the art, this angle will generally be about 7'.

The throat I! of the diffuser duct i8 is provided with an inlet orifice b which has a sharp edge on the inlet side thereof and is therefore of the type commonly designated as sharp-edged. It is well known in the art that such sharpedged orifice has a relatively low orifice coeifi cient for the normal flow of fluid therethrough from a body of fluid which is in extended contact with the margin of the orifice on the inlet side thereof. Eddy currents are produced at the inlet of the diffuser by the rapid increase in the area of the actual fluid flow path through the diffuser, which eddy currents are introduced by the contraction of the fluid stream entering the throat I! at an angle to the axis of the difl'user and through the sharp edges of orifice b.

Opposite the inlet I! of duct I6 is a conduit 20 having an inwardly converging bell-shaped inlet 2| and an outlet in the form of a round edged discharge orifice a. The inlet 2! of conduit 20 is disposed in opposed relationship to the outlet 22 of duct II and spaced therefrom as indicated at 23 while the discharge orifice a is in axial alignment with the inlet ll of duct i8 and spaced therefrom as indicated at S. For best operation of the apparatus it is preferable that the inlet 13 of conduit 20 have a slightly greater area than the outlet 22 of duct ll. The axial alignment of orifices a and b provides for the projection of fluid from conduit 20 into duct l8 and it is preferable also, for reasons which will become apparent hereinafter, that the orifice a, which is of the round-edged type and which therefore has a relatively high orifice coeflicient, should have also a slightly larger area than that of the orifice b and a circular crosssectional shape to correspond with the circular cross section of the duct l8.

For a more detailed description of the arrangement of duct l6 and its cooperating'oriflces and of the manner of determining the various dimensions and spacings of the apparatus, reference may be had to my previously referred .to copending application. However, sufficient of the details of arrangement and operation of the apparatus will be given herein to insure an adequate understanding of the specific invention to which .the present application is directed.

For the purpose of describing the operation of the apparatus embodying the present invention, attention is directed particularly to Figs. 2' and 3, and it will be assumed that the apparatus therein illustrated is to be employed to control the flow of air to a space C, adjacent the outlet l8 of the duct it, from a spaceA interiorly of conduit 20 and from atmosphere which is designated as the space B surrounding the apparatus. If the space A within conduit 20 is subjected to a positive pressure, a pressure above atmospheric,

air is discharged therefrom through orifice a into the orifice b at the throat I! of diffuser duct l8. Also, if the space C at the discharge end It of duct I6 is subjected to negative pressure, a pressure below atmospheric, there is a tendency for air to be drawn into the throat H of the difluser through the space 8 from atmosphere B, and as will be pointed out hereinafter, the amount of air drawn in from atmosphere depends principally upon the difference between the pressures of space A and of space B. When space C is under negative pressure and space A under positive pressure, a stream of air is discharged through orifice a into the throat I! of duct It as indicated by the arrows in Fig. 2 which are representative of the flow lines of the air stream. Since in the illustrated embodiment the orifice a is slightly larger than the orifice b and has the same cross-sectional shape, the rim of orifice b operates to core out the central portion of the stream discharged from orifice a and the outside portions or laminae of the stream are discharged outwardly through the space S and flow along the outer wall of the diffuser duct it. This outer portion of the air stream flowing on the outside of the diffuser overcomes or blocks any tendency for air to be entrained into the inlet of the diffuser from the atmosphere B through the space S by means of the injector action of the stream flowing through the inlet of the diffuser. Consequently, the central portion of the stream flows into the inlet of the diffuser and is substantially uniformly distributed across the area thereof with all portions of the stream flowing at substantially uniform velocity and along lines substantially parallel to the axis of the diffuser. By proper adjustment'of the sizes of orifices a and b and of space S with relation to each other, the discharge of air externally of the throat of the diffuser may be reduced to a minimum while the blocking effect thereof is maintained.

Under the conditions outlined in the previous paragraph, the orifice a in effect becomes the inlet of the difl'user and therefore the inlet orifice coefllcient of the diffuser is substantially unity. Hence, the stream of air enters the throat of the diffuser with very slight loss in head and with substantially no contraction. Also, the diffuser being designed as previously pointed out so that it has maximum efficiency of operation when a fiuidstrearn enters the throat thereof as just described, there being no eddy currents induced at the inlet thereof and the fluid stream flowing smoothly therethrough as indicated by the arrows in Fig. 2, the loss in head across the diffuser is a minimum. Consequently, under the positive pressure conditions a minimum of impedance is imposed to flow of air from the space A interiorly of conduit 20 to the space designated C, and for a given pressure drop across the apparatus a maximum air flow is secured.

On the other hand, when space A is under atmospheric pressure and space C is subjected to negative pressure, pressure lower than atmospheric, by any suitable means, a stream of air is no longer discharged from the orifice a into the throat I! of the diffuser I! in the manner previously described and the flow of air into the throat of the diffuser from atmosphere 3 through the space S is nolonger blocked off. The orifice b then becomes the efl'ective inlet of the diffuser and air fiows from atmosphere into the diffuser at a relatively large angle to the axis thereof, as indicated by the arrows in Fig. 3, so that the low orifice coefficient at the diffuser inlet results aocaau condition outlined in the previous paragraph.

In addition the contraction of the air stream entering the difl'user through the orifice b produces eddy currents along the walls of the diffuser, as

indicated by the arrows in Fig. 3, which impede the flow of air through the difl'user and. cause ineflicient operation thereof and a consequent larger loss'in head thereacross. The total loss in head across the apparatus under the negative pressure conditions due to'the effect of the sharpedged orifice b and the inefilcient operation of the diffuser ismany times larger than the total loss in head across the apparatus under the positive pressure conditions. In fact, it has been ascertained that the magnitudes of negative pressure required to produce given rates of air flow through the apparatus are in the neighborhoodoi' 18 to 20 times greater than the magnitudes of positive pressure necessary to produce the same rates of air flow throughthe apparatus. When the space C is subjected to a constant negative pressure at the same time that the space A is subjected to a variable positive pressure, as the pressure within the space A decreases the force of the discharge through the orifice a also decreases with resultant decrease in the blocking effect produced thereby at the space designated S. A point isreached atwhich air begins to flow in increasing quantities through space S from atmosphere B into thethroat I! of the difluser I3 and the impedance to the flow of air through the diffuser thereafter increases as the pressure in spaced decreases. Henceit'will be seen that variation .of the differential between thepressure of space A and space B intermediate zero difler-. ential and thediiferential at whichair just begins to flow into the diffuser inlet from space B, produces variation in the impedance to flow through the diifuser which'is inversely in proportion to a function of the difierential.

From an understanding of theprinciples underlying mywinvention as set forth in the foregoing,

discussion and as set forth morein detail in my previously referred to copendlng application, it

will be evident to one skilled in the art that the 2 present invention is not limited to the exemplary forms of the discharge orifice a, space S and diffuser ductfl 6 described and illustrated herein, and

that the apparatus for practicing the invention may take various forms whereby may be secured different degrees of variation in impedance or restriction of the fluid flowthrough the apparatus .upon changeover from positive to negative pressureconditions or vice versa. i

In order tocirculate air through casing l2 and over the heat dissipating device l0, there is provided a fan 24 located in the inlet l of 'duct I3 and driven by means of an electric motor 25 which is connected to be energized from electric supply line 26. This fan 24 serves also to impose a negative pressure upon the space C. A similar fan 21 is located in conduit 20 adjacent the inlet 2| thereof and is arranged tobe driven by means i of an electric motor 28, also connected to be energ zed from supply line 26. Motor 25 is connected directly to supply line 26 in order that when energized it rotates at constant speed. causing fan 24 to force a constant volume of air into the intake duct l3 and through casing l2. On the other hand, it is desirablefor reasons to be given hereinafter that fan 21 be operated at: different speeds and hence motor 28.is connected to supply line 26 through some form of speedcontroldevice,

contactmechanism 3| diagrammatically shown in Fig. 1: Contact 3| is mounted on the movable end of a thermostatic device 32 which is represented for example as being of the expansible fluid bellows type *having one end 33 thereof extending within casing l2 in proximity to the heat dissipating devicellil to be responsive to the heat dissipated j-therefrom during operation. The resistanee 30, contact 3|, and thermostatic device 32, constitute'a thermal responsive speed control device for motor 28. Both motor 25 andmotor 11%;! beddisconnected from supply line 26 by mea s of a manually operable switch 34.

s The apparatus illustrated in Flg. l'may be employed to maintain the electric discharge device In ata certain constant temperature or within a certain temperature range regardless of the ambient temperature outside casing l2. This is accomplishedby varying the proportions of recirculated air and makeup air supplied to the casing by means of fan 24. Under certain conditions the amount of recirculated air must be substantiallyzero and for other conditions the amount of. makeup airmust be substantially zero. Intermediate those extreme conditions it is desirableflto-obtain variations of the relative proportions of recirculated and makeup air in acon the electricndischargedeviceand variations in the. ambient temperature surrounding casing l 2. Motor,25 and fan 24 operate atconstant speed, when switch-34 is closed, to supply a, constant volume -of coo1ing air through casing I2. The function of fan2i' and motor 28is 'tocontrol the proportions of recirculated air and fresh air going to make up this constant volume of air supplied to casing l2. The energization of motor 28 and the speed of operation of fan 21 are controlled by means of the cooperative action of the variable resistance 30 and movable contact 3| which is movable inhaccordance with temperature variations within casing l2.

The thermostatic device 32 may be so adjusted that when electric discha e device It), is oper ating at a proper temperature, all of resistance 30 is cut out sotliat motor 28 receives maximum exdescribed, that theimpedance imposed to the flow of the recirculated air through orifice h and dif fuser I 6 is a minimum. This 'recirculated air therefore is supplied in large volume to the space C at the outlet I8 of the diffuser and constitutes the major portion of the airdrawnintothe intake duct l3 bymeans of fan 24 sothat a very small volume ofmakeup or fresh air is drawn into the inlet 15 of duct l3from atmosphere through the-space designatedlfl.

On the other hand, when the temperature of the air surrounding the electric discharge device l0 reaches a predetermined high'limiting degree, thermostaticf element 32 operates to insert a maximum of resistance 30 or to completely open the circuit of motor 28 so that it will operate at its lowest speed or not at all. Under these conditions fan 21 andrestricted orifice a offer such impedance to flow of air through conduit 20 that Also, since fan 21 no longer operates to discharge any appreciable stream of air through the orifice a into the orifice b, the space Sis no longer blocked ofi andair flows there'through-intothe inlet orifice b of diffuser ii at anlangleto the axis of the'diifuser and, as previously described, imposes a high impedance to fiow oi. air through the diiiuser and thus further decrease the, volume of spent air passing from the duct ll through conduit 20 and difiuser ii to the inlet II of duct l3. Hence, since the impedance to fiow'oi air through the diiluser is now at its maximum, fan 24, in order to force a constant volume of cooling air through duct l3 and casing i2, draws a. large volume of makeup air from atmosphere. into the inlet l5 of duct I: through space l9,,thus providing maximum cooling of the electric discharge device Ill.

For temperatures of the electric discharge device intermediate the limits previously mentioned, the thermostatic element 32 operates'to insert varying amounts of resistance 30 into the circuit of motor 28 which results in the operation of the motor at variable speeds and fan 21 is effective to discharge varying amounts of spent or recirculated air through the orifice a into the inlet of diffuser l6. Under these conditions, the impedance to flow of spent air through the difiuser varies substantially inversely in proportion to the amount of said air which is discharged from orifice a, and the amount of makeup air drawn into the inlet, I5 of duct l3 through space l9 varies substantially inversely in proportion to the amount of air passing through the difluser duct. Hence it will be seen that the fiow control apparatus of the presentv inventionprovides a'very sensitive control of the relative proportions'of recirculated and makeup air supplied to casing H for cooling the electric discharge device II) or other heat dissipating device and accomplishes this control without employing movable parts such as the usual movable vanes and shutters.

While I have shown and described my present invention in connection with a specific embodiment thereof, it is to be understood that I do not wish to be limited to the details of the illustrated embodiment since it is apparent that the principles herein disclosed are "susceptible of numerous other applications, andthalt modifications may be made in the arrangement and structure of the elements of the fluid flow control apparatus without departing from the spirit and scope of my invention as definedin the appended claims. a r y 7 What I claim as new and desire to secure by Letters Patent of the United Statesls:

1. In combination, an enclosure having an intake opening, means for drawing air into said opening and circulating the air through the enclosure, means for conducting air to said opening including a fluid pressure diffuser duct having its outlet end in opposed spaced proximity to said opening and having its inlet in the form of a substantially sharp-edged orifice, means for exhausting from said'enclosure a portion of the air circulated therethrough and for discharging said portion of air into the inlet orifice of said diffuser duct in the form of a streamsubstantially uniformly distributed over the area of the inlet orifice with all parts of the stream flowing at substantially equal velocities along lines substantially parallel to the axis of the inlet orifice, means providingfor the release fromthe enclosure of the remainder of the air circulated through .the enclosure, and means for varying the operation of said discharging means.

2. In a ventilation system, the combination oi an enclosure to be ventilated having intake means communicating with atmosphere, a duct having an inlet in the form of a sharp-edged orifice and an outlet in communication with said intake means, means operable for circulating a substantially constant volume of air through the enclosure from said intake means and for creating a negative pressure at the outlet of said duct, means variably operable for exhausting variable portions of said volume of circulated air from the enclosure and for discharging said portions of circulated airinto the inlet orifice of said duct in the form of a stream substantially uniformly distributed over the area of the orifice with all parts of the stream flowing at substantially equal velocities along lines substantially parallel to the axis of the orifice, means providing for the relief of the remainder of the circulated air to atmosphere and means operative responsively to vari-, ation in a predetermined condition within the enclosure for controlling the operation of said variably operable means to thereby vary the quantity of circulated air discharged into said duct.

3. In a ventilation system, the combination of an enclosure to be ventilated having air intake means communicating with atmosphere and air exhaust means including means providing relief to atmosphere and other means providing a discharge orifice, means ior circulating a substantially constant volume of air through the enclosure, means variably operable for discharging variable portions of said volume of circulated air from the enclosure through said orifice, means for returning circulated air through the enclosure including a fluid duct having a sharp-edged inlet orifice in axially aligned spaced relation with said first orifice to receive the circulated air discharged therefrom and also having substantially smooth inner walls extending from said inlet orifice with an outlet in communication with said intake means, said inlet orifice having less area than and substantially the same cross sectional shape as said first orifice, and means operative responsively to variations oi a predetermined condition within the enclosure for varying the operation of said variably operable means to thereby regulate the volume of circulated air discharged from said first orifice into the inlet orifice of said duct.

4. A ventilation system including in combination an enclosure to be ventilated having intake and exhaust openings in communication with atmosphere and a fan operable for drawing a substantially constant volume of air in through said intake opening and to circulate said volume or air through the enclosure, a hollow casing having an inlet in spaced relation with said exhaust opening to receive circulated air therefrom and having an outlet in the form of a fluid discharge orifice, a second fan operable for causing fiow of circulated air from said exhaust opening into said casing and for discharging said last 'mentioned air from said casing through said orifice, a fluid duct having an inlet in the form of sharpedged orifice in spaced axial alignment with said first orifice to receive air discharged therefrom and having an outlet disposed to discharge air from said duct adjacent said intake opening, said orifices having substantially the same cross sectional shape with said inlet orifice having less area than said discharge orifice, and means op- 2,095,824 erative responsively to variations in a predetermined condition within the enclosure ior varying the operation of said second fan to thereby vary the quantities of circulated air discharged from said casinginto said ducts and thence into proximity to said intake means.

'5. In a ventilation system, the combination of an enclosure to be ventilated having air intake means communicating with atmosphere and air exhaust means including means providing relief to atmosphere and other means providing a fluid discharge orifice, means for circulating a substanvariable portions of said volume of circulated air i from the enclosure through said orifice, means for returning circulated air to the enclosure including a diffuser duct having its inlet in axially aligned spaced relation with said orifice to receive the circulatedair discharged therefrom and its outlet in communication with said intake means, the inlet of said diffusing duct having less area than and substantially the same cross sec-- tional shape as said orifice, and means operative responsively to variations of a predetermined condition within the enclosure for varying the operation of said variably operable means to thereby vary the amount of circulated air discharged from said orifice into the inlet of said diffusing duct.

KENION D. McMAHAN. 

